1. Field of the Invention
The present invention relates to an optical scanning device which scans, through a light waveguide array, image information light emitted from a light source.
2. Description of the Related Art
There have heretofore been optical scanning devices in which image information light emitted from a light source is written on a photosensitive recording medium by scanning, for example, through an optical fiber waveguide array, the light on the surface of the medium.
As shown in FIG. 3, a conventional optical scanning device 10 includes a point light source 20, a scanner 30, and an optical fiber array 40. The point light source 20 is composed of a semiconductor laser (hereinafter referred to as an LD) or a light emitting diode (hereinafter referred to as an LED), both of which are driven by image signals. The sccanner 30 has an optical waveguide 33 to scam light received from the point light source 20, this scanning being performed at an equiangular speed in the circumference direction of the scanner 30. The optical fiber array 40 carries the light scanned by the scanner 30 to a photosensitive drum 50.
The scanner 30 is rotated at a fixed speed due to the fact that a rotary body 32, in which the optical waveguide 33 is embedded, is rotated by a motor 31. In the optical waveguide 33, the light entrance lies on the axis which coincides with the rotating center of the scanner 30, whereas the light exit extends in the redial direction of the rotary body 32, and leads to the periphery of the scanner 30.
A light incoming opening of the optical fiber array 40 is arc-shaped so as to surround the scanner 30; a light outgoing end of the optical fiber array 40 is linearly arranged in the direction of the axis of the photosensitive drum 50. With the above arrangement, optical signals are converted from a circular form to a linear form.
As an optical waveguide array other than the above-described array in which a plurality of optical fibers are arranged, there is also a multi-mode waveguide array utilizing selective photopolymerization of macromolecular materials. A manufacturing method of the multi-mode waveguide array will now be described with reference to FIG.
4. The details of the manufacturing method are as follows: (a) forming a base film: methyl acrylate, a photosensitive material as a dope monomer whose refractive index is n2=1.48, is contained in polycarbonate as whose refractive index is n1=1.59. A melt extraction method (known also as casting) is used to form a sheet with a thickness of 50-100 .mu.m.
(b) selective photopolymerization by mask exposure: a pattern mask is laid over the sheet so that parts in which light waveguides are to be aranged may intercept light. Ultraviolet rays are then irradiated and these parts are exposed. The methyl acrylate is thus photopolymerized only in the exposed parts, whereby the mask patterns are transcribed.
(c) removing unreacted monomers: after the remaining monomers in the unexposed parts have been removed by vacuum drying, only polycarbonate in the matrix of the unexposed parts remains, and the unexposed parts turn into core sections 100a whose refractive index is 1.59. The refractive index of the exposed parts falls because of the photopolymerization mentioned above, and the exposed parts turn into clad sections 100b.
(d) cladding on the surface: the upper and lower sides of the sheet are coated with acrylic resin with a low refractive index to form two clad layers 100c, 100c.
By the above-described manufacturing method, an array is formed in which a number of optical waveguides, each having a width and height of several tens of microns, are arranged in rows. The feature of such optical waveguides is that they all are transparent, with the transparency thereof ranging from visible light to infrared rays in the vicinity of 1.6 .mu.m wavelength. The propagation loss of the optical waveguides is about 0.2 dB/cm.
In the optical scanning device using the above multi-mode waveguide array, however, light transmission efficiency varies with factors, such as different lengths of the optical waveguides, differences in bulk loss during the manufacturing process, and differences in reflectivity on the ends on which light impinges and from which the light emanates. This results in a problem in that the intensity of a light beam, emitted from the light outgoing end of the respective optical waveguides, varies. This problem cannot be neglected since it appreciably influences the printing quality.